As an electric motor, for example, there is a brush-attached electric motor in which a plurality of permanent magnets are disposed at an inner circumferential surface of a bottomed cylindrical yoke, and an armature is rotatably installed further inside in a radial direction than the permanent magnets. The armature has an armature core fitted onto and fixed to a rotary shaft, and a commutator in which a plurality of segments are disposed. A plurality of teeth extending outward in the radial direction are installed at the armature core, and a plurality of slots elongated in the axial direction are formed between the teeth. A winding is inserted through these slots, and the winding is wound on the teeth through an concentrated winding method or a distributed winding method.
The winding is electrically connected to the segments of the commutator. Each of the segments is configured to come in sliding contact with a brush configured to supply electricity, and current is supplied to the winding via the brush.
When the current is supplied to the winding, a magnetic field is formed, and the armature is rotated by a magnetic attractive force or repulsive force generated between the magnetic field and the permanent magnet.
In recent years, in an electric motor having the above-mentioned configuration, further miniaturization and high performance have been required. Here, for example, an electric motor in which anisotropic rare earth element bond magnets formed of an NdFeB (neodymium-iron-boron)-based magnet powder are installed at four poles is proposed. In this way, as permanent magnets of rare earth elements having a high magnetic force are multipolarized, miniaturization and high performance of the electric motor can be attempted (for example, see Patent Literature 1).
In addition, in an electric motor in recent years, various elements have been mounted from the viewpoint of requirements of high performance, fail-safe characteristics, and so on.
For example, an electric motor including a substantially bottomed cylindrical yoke and an end bracket having a connector section and fixed to close the yoke, and in which a thermistor and a noise prevention element (corresponding to “a condenser” and “a choke coil” of the present invention) are mounted on the end bracket has been proposed (for example, see Patent Literature 2).
As in the distributed winding method, when the winding is wound between the slots disposed at predetermined intervals, the coil wound later is wound further outside in the radial direction than the coil wound first. That is, the coil wound in a post-process is disposed at an opening side in the slots. In addition, a specific slot accommodates the winding wound first and the winding wound second, and a specific slot accommodates the winding wound last and the winding wound second to last. For this reason, when all of the slots are formed in the same shape, an ineffective space is generated at each of the slots, and a position and a state of the coil become unstable. As a result, rotation imbalance of the armature may occur.
A technology is disclosed in which a rotary shaft (shaft)-side bottom surface of the slot between the coils wound first is formed substantially along an outer circumferential side line of an armature core of the coil (for example, see Patent Literature 3). Accordingly, the shaft-side end section of the coil can come in contact with the shaft-side bottom surface of each of the slots, and generation of the useless space of each of the slots can be prevented. For this reason, generation of instability of the position and state of the coil due to the space can be prevented. As a result, generation of rotation imbalance of the armature can be prevented.